A photosensitive composition comprising an o-quinonediazide compound has been used industrially as a very excellent positive working photosensitive composition in the production of a lithographic printing plate or as a photoresist. For increasing the sensitivity of the positive working photosensitive composition comprising an o-quinonediazide compound, various proposals have been hitherto made. However, it is yet unsuccessful to provide a composition having not only a high contrast image-forming ability but also satisfactory performance in halation, safe light tolerance and development latitude, without lowering the sensitivity.
For instance, the reduction in the content of an o-quinonediazide compound increases the sensitivity, but lowers the contrast of an image and causes deterioration in halation, safe light tolerance and development latitude. Similarly, the use of the combination of an o-quinonediazide compound and a binder having high solubility in an alkali increases the sensitivity, but results in an image having low contrast and deterioration in halation, safe light tolerance, and development latitude.
On the other hand, chemically amplified photosensitive materials having an alkali-soluble group protected by an acid decomposable group has been proposed as a system having a higher sensitivity than o-quinonediazide compounds, e.g., in U.S. Pat. No. 4,491,628 and European Patent 0,249,139, and have been used prevailingly. However, these materials are still unsatisfactory as to the image contrast and the development latitude.
The term "soft" used for the image contrast means that, when a coating of photosensitive composition is exposed through a step wedge and then developed, there is a great difference between the step number at which an image begins to remain and the step number at which the coating remains entirely. Conversely, the term "hard" used for the image contrast means that there is a small difference between the step number at which an image begins to remain and the step number at which the coating remains entirely.
The terminology "halation" as used herein means that the nitrogen produced by the decomposition of a quinonediazide compound lifts the lith film out of the substrate and thereby it is made impossible to subject the lith film to perfect contact exposure; as a result, a halation (under cutting) is generated. In general, under a condition that the photosensitive compositions have the same clear sensitivity, the generation of such a halation can be prevented more easily in a composition which provides an image having a higher contrast.
The terminology "safe light tolerance" as used herein means that the image sensitivity of a printing plate is insusceptible to the influence of exposure to white light, such as light of a fluorescent lamp, and the safe light tolerance becomes better the higher the image contrast is. This tendency is attributable to a partial decomposition of a quinonediazide compound under white light. As far as a printing plate can provide a high contrast image, the image is not eluted even when a small amount of quinonediazide compound is decomposed, so that the printing plate forms a similar image whether or not it has undergone the exposure to white light.
The terminology "step wedge" as used herein refers to the strip-form film having the density changed stepwise by 0.15 for each step. The step wedge is used for examining the relationship between the amount of exposure and the amount of the photosensitive layer remained after exposure and development. The term "clear sensitivity" as used herein refers to the sensitivity at which the image begins to form after exposure and development.
The terminology "development latitude" as used herein means the measure of a variation caused in image sensitivity by the change in concentration of a developer used after exposure. The smaller the variation in sensitivity is, the better the development latitude is.
Further, the technique of increasing the sensitivity by adding a light-insensitive compound to a photosensitive composition comprising an o-quinonediazide compound has been proposed, but has various drawbacks.
For instance, the addition of cyclic acid anhydrides for increasing the sensitivity is proposed in JP-A-52-80022 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). This method actually has a sensitivity increasing effect, but the addition of such an acid anhydride in a sufficient amount to provide a considerably increased sensitivity lowers the image contrast and causes marked deterioration in safe light tolerance and development latitude. In addition, it is proposed in JP-A-55-73045 to add a hydroxybenzophenone-formaldehyde condensation product for the purpose of increasing the sensitivity. This proposal also has the same drawbacks as the proposal by JP-A-52-80022. Namely, when the condensation product is added in a sufficient amount to increase the sensitivity to a considerable extent, the image contrast is lowered and safe light tolerance and development latitude are deteriorated seriously.
With the intention of solving the aforementioned problems, some methods of adding surfactants have been proposed. For instance, JP-A-59-121044 discloses the method of widening the development latitude by the addition of an amphoteric surfactant and an organic boron-containing surfactant to a highly sensitized positive working photosensitive composition, and JP-A-62-251740 discloses the method of widening the development latitude by the addition of a nonionic surfactant to a highly sensitized positive working photosensitive composition. However, each of those methods can bring about some improving effect upon development latitude, but the effect is not satisfactory. The increase of the amount of such a surfactant to attain a sufficient effect causes a drop in the sensitivity. On the other hand, those methods have no effect of improving the halation and safe light tolerance.
Furthermore, the fluorine-containing polymers having a fluoroaliphatic group and a polyoxyalkylene group are described as surfactants in JP-A-62-226143, JP-A-3-172849 and JP-A-8-15858. However, the use of those polymers can not provide improvement in halation and safe light tolerance.